Exercising and sport have been practiced for millennia, and there are legions of devices which are utilized to enhance such exercising and physical training for sport. It has long been accepted that weight training has beneficial physiological effects on the body.
Muscle groups can be classified into three groups: primary movers, stabilizers (secondary), and neutralizers (tertiary)—in which, their responsibility and role changes based on the body's orientation. When the body is young, it has a natural propensity to call upon and fire most of our muscles—giving us a great sense of balance. As we age, it becomes increasing more difficult to access and recruit the vital secondary and tertiary muscle systems.
As a general statement, most training devices are directed at strength of large muscle groups (weights, etc.) and/or timing of large physical actions (sport training devices), with relatively fewer devices directed at balance and the coordination of the secondary or tertiary muscles used in balance relative to the larger muscle groups. Within the category of balance enhancing devices, some devices incorporate rolling balance by virtue of a curved or spherical profile. In some sports, such as surfing or skateboarding, balance is practiced and achieved on a relatively unstable device through two points of human contact, i.e., by balancing with two feet on a surfboard.
The exact physical phenomenon which occurs in muscles to achieve balance is the subject of considerable study. Within each human body there are countless sensory receptors which are constantly monitoring our orientation and our interaction to the environment. Moreover, there is a proprioceptive sensory system designed to detect when the body is under tension or pressure, such as when holding a dumbbell during weight training. The firing of various muscles to keep and maintain balance occurs far too quickly for conscious awareness, and instead occurs reflexively. Part of the balance reflex are includes the Golgi tendon, a proprioceptive receptor which is located within the tendons found on each end of a muscle. The Golgi tendon is stimulated by a quick change in tension on a muscle, to begin the reflexive are for additional muscles to fire to restore balance.
The muscle spindle has a distinct sensory responsibility—that is to monitor the change in length of the muscle and soft tissue. More specifically, this receptor is designed to sense the “rate of change” in respect to length of the muscle. The muscle spindle is best stimulated during a sudden, almost unexpected, involuntary and quick movement. Thus—when a very quick movement is applied to the body—likely for the body to lose equilibrium and balance—a profound counter response is elicited in hopes of restoring balance. Triggering the muscle spindle receptor causes significant and high levels of muscle recruitment and muscle engagement to occur—especially the important and vital secondary and tertiary muscles.
While the science concerning large muscle strength exercises (using weights or other resistance against large muscle contraction) is relatively mature, the science of what exercises to perform and what devices to use to perform those exercises to specifically trigger the Golgi tendon receptor and the muscle spindle receptor—for physiological benefit rather than for sport (such as surfing) performance—is in its infancy.